The one that feels best for you, don't make another n00b thread where people just say their fork is the best and that "the boxxer will snap for freeride" or "the 888 is crap for downhill" or "the fox 40 need very high maitenance". Just save everyone the pain and frustration of trying to shove their oppinions down their throught and actually get out and ride the fork and see what you like.
I'd get a boxxer and be done with it, the damper is great, it's dead easy to service, and sram backs their shit. That and parts are cheap for them when you buy used.
Nothing wrong with the 40 or the 888 though, just be sure it's a newer 888.